Effects of Cold Exposure or TRH on the Serum TSH Levels in the Iron-Deficient Rat

Abstract

Normal and iron-deficient rats were exposed to cold at 4°C for 1 hr or 5 hrs and the serum TSH, T₃ and T₄ levels were compared with those in rats kept at room temperature (20°C). There was a rise in serum TSH, T₃ and T₄ levels in response to 1 hr and 5 hrs of cold exposure in normal, but not in iron-deficient rats. Although pituitary TSH contents were lower in iron-deficient rats, the increases in serum levels of TSH following administration of TRH were similar in both normal and iron-deficient rats. The results suggest that the inability to respond to cold in iron-deficient rats may be due to a reduction in the release of TRH from the hypothalamus.